FIELD OF INVENTION
The present invention relates to a process for detection of leakage in sub cooling
zone of a feed water heater by hydraulically.
BACKGROUND OF THE INVENTION
The feed heaters are used in regenerative steam power cycle to increase the
efficiency and to reduce the cost of the power generation. A high energy steam
from the boiler expands through the turbine where its heat energy is converted
into mechanical energy. It is exhausted into condenser and by losing its heat to
condenser cooling water becomes condensate. This loss of heat represents a
large part of the energy which is added in the boiler by way of burning the fuel.
The feed water heaters extract steam from the turbine and transfer its heat to
the condensate returning to the boiler. The heat recovered in the feed heater is
not rejected from the cycle and, as a result, the thermal efficiency of the cycle is
improved. The feed water heaters are classified as low or high pressure heaters
depending upon their location in the cycle with respect to the Boiler feed pump.
The high pressure heaters contain 3 separate zones of heating such as a de-
superheating zone, a condensing zone and a sub-cooling zone whereas low

pressure feed heaters may contain a condensing/ a condensing plus sub cooling
zones. In a condensing zone, the residual superheat and the latent heat of the
extracted steam is transferred to the condensate. The steam thus gets converted
into liquid called drain. Sub cooling zone is a totally sealed liquid to liquid
exchanger within a heater, in which the sensible heat of the drain is removed by
the passing cold condensate. This heat addition to condensate further improves
the turbine efficiency otherwise this energy would have been lost in condenser.
In a horizontal feed heater with an integral sub-cooling zone, the steam gets
condensed in the condensing zone and the drain is collected at the bottom. The
sub-cooling zones are disposed separately a counter flow baffled heat
exchangers contained within the heater shell. Heat is exchanged between the
drains and the feed water flowing through the tubes. These surfaces are
surrounded by hot water that transfers heat to the drains as they are sub-cooled.
The various components of sub cooling zone comprises one end plate, one
shroud, a partition plate and a stabilization plate are welded together along a
heater shell so as to form a close chamber isolated from the condensing zone.
The entry of drains (condensate) in sub cooling zone is through the bottom.
Level in the heater is so constituted that entry point of sub cooling zone is
always submerged in the condensate and the steam which is present in the
condensing zone does not enter the drain cooling section. The annular space
between the tubes and tube holes in the end plate are potential source of

leakage. The end plate must fit the tube closely, yet provide for tube to slide. A
close fit will restrict the steam flow into the holes to an amount that can
condense by the tube surface within the plate thickness. It is very important that
the shroud be leak tight. Weld, cracks permit steam to enter the zone and can
cause water hammer and reheating of the sub-cooled drains. Welds must be
sound re-building of the bundle. This becomes more critical if such leakage is
detected during operation. Due to typical configuration of sub cooling section, as
a practice no leak testing is foreseen for this section. However, same is done for
the complete heater in horizontal position with shell in position.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process for
detection of leakage in a sub-cooling zone of feed water heater which eliminates
the disadvantages of existing state of art.
Another object of the present invention is to propose a process for detection of
leakage in a sub-cooling zone of feed water heater which gives assurance for
achieving the desired turbine cycle efficiency.

A further object of the present invention is to propose a process for detection of
leakage in a sub-cooling zone of feed water heater which provides smooth
trouble free operation of feed water heater.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows complete horizontal heater with integral sub cooling zone.
Fig.2 - shows various components of sub cooling zone with entry and exit
connections of condensate.
Fig.3 - shows tube bundle in horizontal condition with drain cooler entry on top.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
A feed water heater (1) consists of three main components a shell (2), one Tube
Bundle (3) and one Water box (4). A tube bundle (3) of heater with integral sub
cooling zone (5) further consists of a plurality of tubes (6), a tube support plate
(7), a plurality of baffles, one partition plate (8), one shroud (9), one end plate
(10), one seal plate (11) etc. sub cooling zone (5) is fully isolated from
condensing zone. Weld, cracks permit steam to enter this zone and can cause
water hammer and reheating of the sub-cooled drains (13). It is very important

that shroud (9) be leak tight for optimum performance of the feed water heater
(D-
The leak proofness of sub-cooling zone (5) in a feed heater (1) can be assured
by introduction of water fill test as described below:
a) Placing the tube heater bundle in horizontal position with drain cooler
entry (14) on the top (Fig.3)
b) Blocking the drain outlet (15) connection provided on the skirt
c) Filling the sub-cooling zone (5) with water through water fill point (16)
used for water fill test
d) Observing the drop in water level (17) inside the sub-cooling zone and
small seepage from the end plate area (10).
e) Checking any leakage from sub cooling zone (5)
f) Repairing by welding the leakage point

WE CLAIM
1. A process for detection of leakage in sub-cooling zone of a feed water
heater comprising the steps of:
i) isolating the assembly of sub cooling zone (5) from the feed
water heater unit (1);
ii) placing the tube heater bundle in horizontal position with drain
cooler entry on the top;
iii) blocking the drain outlet connection provided on the skirt;
iv) filling the sub-cooling zone with water through water fill point
used for hydraulic test;
v) observing the drop in water level;
vi) checking any leakage from sub-cooling zone or small seepage
from the end plate area; and
vii) repairing by welding if any leakage exists.
2. The process of detection of leakage in sub-cooling zone as claimed in
claim 1, wherein a sub-cooling zone comprises a plurality of tubes, a tube
plate, a plurality of baffles, one partition plate, one shroud, one end plate
and one seal plate.

3. The process as claimed in claim 1, wherein water fill test is carried.
4. The process of detection of leakage in sub-cooling zone as claimed in
claim 1, wherein the said sub cooling zone is an integrated part of the
feed water heater.

A process for detection of leakage in sub-cooling zone of a feed water heater comprising the steps of isolating the assembly of sub cooling zone (5) from the feed water heater unit (1) and placing the tube heater bundle in horizontal position with drain cooler entry on the top and blocking the drain outlet connection provided on the skirt and filling the sub-cooling zone with water through water fill point used for hydraulic test and observing the drop in water level and checking any leakage from sub-cooling zone or small seepage from the end plate area and repairing by welding if any leakage exists.